Barbershop quartet

A barbershop quartet is an ensemble of four people who sing a cappella in the exacting barbershop music genre. While the form is accessible to nearly anyone who can carry their part, the best quartets are formed of singers with a very uniform sound, particularly for vowels. With few exceptions, quartets are all-male or all-female in order to better match voices. Often siblings are naturally well-matched, as they grow up using the same accent. In other cases, disciplined practice over time yields consistent use of the same vowels.
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Noun
1. an unaccompanied quartet of (usually male) voices singing sentimental songs in four-part harmony
(hypernym) quartet, quartette

QUARTETTO MASCHILE CHE CANTA A CAPPELLA